1. Technical Field
The invention relates to laser engraving, particularly to engraving with galvanometers in a large area.
2. Related Art
Laser processing technology has applied in industry for over several decades, for example, applications of welding and cutting. Particularly in the recent years, compact industrial laser becomes popular due to the progress of laser beam sources, a laser engraving device primarily using Nd-YAG laser (i.e. Laser-Marking) is commonly used in metal processing, hand tools, plastic products, electronic components, ceramics, electroplated goods and various gifts.
A general laser processing technique can be divided into two types, which are shown in FIGS. 1 and 2. As shown in FIG. 1, a laser source 10 is fixed at a fixed position. A workpiece 12 is moved by an X-Y carrier 11 and its moving path is controlled by a laser beam, so that the workpiece 12 can be engraved by the laser source 10. FIG. 2 shows the other type, in which the laser source 10a is guided by galvanometers 13, 14 and then focused by a composite lens 15 onto the workpiece 12a after fast scanning. Thus a desired pattern can be obtained. These two conventional treatments have their respective advantages and drawbacks. The former's advantages are a precision treatment position and allowance of treatment in a large area, but its carrier 11 moves slowly so as to make the whole treatment period too long. Particularly, speed and quality of laser treatment will be reduced when the workpiece 12 is too large in size or weight. Thus, it is not suitable for mass production.
However, when the workpiece 12 is too heavy or large to be moved, the efficiency and quality of the laser processing must be disadvantageously affected. More recently, the pen-writing galvanometric scanner appears in the market. But such an approach makes the processing range and the smallest size of laser spot is limited by the focusing lens of the galvanometer. To enlarge the processing range, the focusing lens must be replaced with a one with different focal length. Besides the smallest size of laser spot, the processing height will be increased and the processing exquisiteness will also be varied. The advantages of the latter are a small-sized guiding system, fast treatment and high accuracy, but its drawback is that the treatment area is limited to the composite lens 15 under the galvanometers 13, 14. As shown in FIG. 2, under a situation of large-sized treatment, the composite lens 15 must adjust its working heights 16, 17, 18 to make the focused minimum laser spot become larger. This will reduce treatment accuracy and increase the buying cost of the composite lens 15.